The death toll from this week's devastating earthquakes in southeastern Turkey and northern Syria is expected to surpass 56,000 people, United Nations emergency relief chief Martin Griffiths said. 

"I think it is difficult to estimate precisely as we need to get under the rubble but I'm sure it will double or more," Griffiths told Sky News. "That's terrifying. This is nature striking back in a really harsh way."

A pair of magnitude 7.8 and 7.5 earthquakes struck nine hours apart on Monday, toppling buildings and destroying structures 

STAGGERING TURKEY EARTHQUAKE DEATH TOLL INCLUDES AT LEAST 3 US CITIZENS: STATE DEPARTMENT

About 13.5 million people live in the most devastated area, which is roughly 310 miles in diameter. The death toll had risen to at least 33,185 on Sunday afternoon. 

A massive search and rescue operation was still in effect on Sunday, with 34,717 Turkish personnel joined by 9,595 personnel from 74 other countries. First responders were using thermal cameras to search for survivors under piles of concrete. 

Turkish officials, meanwhile, have started pointing to faulty construction and lax building codes for the scope of the devastation. 

At least 131 people were under investigation for their role in constructing buildings that collapsed during the quake, Justice Minister Bekir Bozdag said Sunday. 

The Associated Press contributed to this report.